A macrocyclic lactone can be derived from a long-chain .omega.-hydroxycarboxylic acid through intramolecular cyclization. Such macrocyclic lactones as cyclopentadecanolide and cyclohexadecanolide are important materials for preparing musk odor. It is known that 2-(.omega.-alkoxycarbonyl alkanoyl)-4-butanolide can be converted into a long-chain .omega.-hydroxycarboxylic acid through hydrolysis, decarboxylation, and subsequent reduction of the carbonyl group. The present invention relates to a method for producing a long-chain .omega.-hydroxycarboxylic acid, which is an intermediate to macrocyclic lactones, and 2-(.omega.-alkoxycarbonyl alkanoyl)-4-butanolide, which is an intermediate to said acid.
Conventionally, there have been many known methods to synthesize long-chain .omega.-hydroxycarboxylic acids such as 15-hydroxypentadecanoic acid and 16-hydroxyhexadecanoic. An example is the method disclosed in Dutch Patent 67, 458 (1951) [Polak and Schwarz] C. A. 45 9076 (1951). This method, however, needs as many as ten steps to produce a long-chain .omega.-bromoxylic acid, which is hydrolyzed into a long-chain .omega.-hydroxycarboxylic acid. This cannot provide a satisfactory industrial process because of the need for many steps for synthesis, relatively low availability of material substances, and hence, unsuitability for industrial mass-production.
Another known method is disclosed in Japanese Patent Laid-Open (Kokai) HEI 5-86013, which uses a .omega.-cyano fatty ester and .gamma.-butyrolactone as starting materials. Specifically, 11-methyl cyanoundecanoate reacts with .gamma.-butyrolactone in the presense of an alkali metal alcoholate to produce .alpha.-(11-cyanoundecanoyl)-.gamma.-butyrolactone, which is then hydrolyzed into 15-hydroxy-12-ketopentadecanonitrile, followed by isolation, secondary hydrolysis, and reduction to provide 15-hydroxypentadecanoic acid.
This method, though being a good one, is still not sufficiently satisfactory because many of the starting materials are not readily available and also because 11-methyl cyanoundecanoate, which is relatively high in price, has to be used as a material. Another problem, though not very serious, is that the nitrile group at the .omega.-position has to be converted finally into a carboxyl group.